Induction of volatile organic compounds in chrysanthemum plants following infection by Rhizoctonia solani.

This study investigated the effects of Rhizoctonia solani J.G. Kühn infestation on the volatile organic compound (VOC) emissions and biochemical composition of ten cultivars of chrysanthemum (Chrysanthemum × morifolium /Ramat./ Hemsl.) to bring new insights for future disease management strategies and the development of resistant chrysanthemum cultivars. The chrysanthemum plants were propagated vegetatively and cultivated in a greenhouse under semi-controlled conditions. VOCs emitted by the plants were collected using a specialized system and analyzed by gas chromatography/mass spectrometry. Biochemical analyses of the leaves were performed, including the extraction and quantification of chlorophylls, carotenoids, and phenolic compounds. The emission of VOCs varied among the cultivars, with some cultivars producing a wider range of VOCs compared to others. The analysis of the VOC emissions from control plants revealed differences in both their quality and quantity among the tested cultivars. R. solani infection influenced the VOC emissions, with different cultivars exhibiting varying responses to the infection. Statistical analyses confirmed the significant effects of cultivar, collection time, and their interaction on the VOCs. Correlation analyses revealed positive relationships between certain pairs of VOCs. The results show significant differences in the biochemical composition among the cultivars, with variations in chlorophyll, carotenoids, and phenolic compounds content. Interestingly, R. solani soil and leaf infestation decreased the content of carotenoids in chrysanthemums. Plants subjected to soil infestation were characterized with the highest content of phenolics. This study unveils alterations in the volatile and biochemical responses of chrysanthemum plants to R. solani infestation, which can contribute to the development of strategies for disease management and the improvement of chrysanthemum cultivars with enhanced resistance to R. solani.

CmDOF18 positively regulates salinity tolerance in Chrysanthemum morifolium by activating the oxidoreductase system.

BACKGROUND: Chrysanthemum, one of the four major cut flowers all over the world, is very sensitive to salinity during cultivation. DNA binding with one finger (DOF) transcription factors play important roles in biological processes in plants. The response mechanism of CmDOF18 from chrysanthemum to salt stress remains unclear. RESULTS: In this study, CmDOF18 was cloned from Chrysanthemum morifolium, and its expression was induced by salinity stress. The gene encodes a 291-amino acid protein with a typical DOF domain. CmDOF18 was localized to the nucleus in onion epidermal cells and showed transcriptional activation in yeast. CmDOF18 transgenic plants were generated to identify the role of this gene in resistance to salinity treatment. Chrysanthemum plants overexpressing CmDOF18 were more resistant to salinity stress than wild-type plants. Under salinity stress, the malondialdehyde content and leaf electrolyte conductivity in CmDOF18-overexpressing transgenic plants were lower than those in wild-type plants, while the proline content, chlorophyll content, superoxide dismutase activity and peroxidase activity were higher than those in wild-type plants. The opposite findings were observed in gene-silenced plants compared with wild-type plants. The gene expression levels of oxidoreductase increased in CmDOF18-overexpressing transgenic plants but decreased in CmDOF18-SRDX gene-silenced transgenic plants. CONCLUSION: In summary, we analyzed the function of CmDOF18 from chrysanthemum, which may regulate salinity stress in plants, possibly due to its role in the regulation of oxidoreductase.

A GASA Protein Family Gene, CmGEG, Inhibits Petal Growth in Chrysanthemum.

The diversity in the petal morphology of chrysanthemums makes this species an excellent model for investigating the regulation mechanisms of petal size. However, our understanding of the molecular regulation of petal growth in chrysanthemums remains limited. The GASA (gibberellic acid [GA]-stimulated Arabidopsis) protein plays a significant role in various aspects of plant growth and development. Previous studies have indicated that GEG (a gerbera homolog of the gibberellin-stimulated transcript 1 [GAST1] from tomato) is involved in regulating ray petal growth by inhibiting cell expansion in gerberas. In this study, we successfully cloned the GASA family gene from chrysanthemums, naming it CmGEG, which shares 81.4% homology with GEG. Our spatiotemporal expression analysis revealed that CmGEG is expressed in all tissues, with the highest expression levels observed in the ray florets, particularly during the later stages of development. Through transformation experiments, we demonstrated that CmGEG inhibits petal elongation in chrysanthemums. Further observations indicated that CmGEG restricts cell elongation in the top, middle, and basal regions of the petals. To investigate the relationship between CmGEG and GA in petal growth, we conducted a hormone treatment assay using detached chrysanthemum petals. Our results showed that GA promotes petal elongation while downregulating CmGEG expression. In conclusion, the constrained growth of chrysanthemum petals may be attributed to the inhibition of cell elongation by CmGEG, a process regulated by GA.

The BTB/TAZ domain-containing protein CmBT1-mediated CmANR1 ubiquitination negatively regulates root development in chrysanthemum.

Roots are fundamental for plants to adapt to variable environmental conditions. The development of a robust root system is orchestrated by numerous genetic determinants and, among them, the MADS-box gene ANR1 has garnered substantial attention. Prior research has demonstrated that, in chrysanthemum, CmANR1 positively regulates root system development. Nevertheless, the upstream regulators involved in the CmANR1-mediated regulation of root development remain unidentified. In this study, we successfully identified bric-a-brac, tramtrack and broad (BTB) and transcription adapter putative zinc finger (TAZ) domain protein CmBT1 as the interacting partner of CmANR1 through a yeast-two-hybrid (Y2H) screening library. Furthermore, we validated this physical interaction through bimolecular fluorescence complementation and pull-down assays. Functional assays revealed that CmBT1 exerted a negative influence on root development in chrysanthemum. In both in vitro and in vivo assays, it was evident that CmBT1 mediated the ubiquitination of CmANR1 through the ubiquitin/26S proteasome pathway. This ubiquitination subsequently led to the degradation of the CmANR1 protein and a reduction in the transcription of CmANR1-targeted gene CmPIN2, which was crucial for root development in chrysanthemum. Genetic analysis suggested that CmBT1 modulated root development, at least in part, by regulating the level of CmANR1 protein. Collectively, these findings shed new light on the regulatory role of CmBT1 in degrading CmANR1 through ubiquitination, thereby repressing the expression of its targeted gene and inhibiting root development in chrysanthemum.

Overexpression of the Chrysanthemum lavandulifolium ROS1 gene promotes flowering in Arabidopsis thaliana by reducing the methylation level of CONSTANS.

DNA demethylation is involved in the regulation of flowering in plants, yet the underlying molecular mechanisms remain largely unexplored. The RELEASE OF SILENCING 1 (ROS1) gene, encoding a DNA demethyltransferase, plays key roles in many developmental processes. In this study, the ROS1 gene was isolated from Chrysanthemum lavandulifolium, where it was strongly expressed in the leaves, buds and flowers. Overexpression of the ClROS1 gene caused an early flowering phenotype in Arabidopsis thaliana. RNA-seq analysis of the transgenic plants revealed that differentially expressed genes (DEGs) were significantly enriched in the circadian rhythm pathway and that the positive regulator of flowering, CONSTANS (CO), was up-regulated. Additionally, whole-genome bisulphite sequencing (WGBS), PCR following methylation-dependent digestion with the enzyme McrBC, and bisulfite sequencing PCR (BSP) confirmed that the methylation level of the AtCO promoter was reduced, specifically in CG context. Overall, our results demonstrated that ClROS1 accelerates flowering by reducing the methylation level of the AtCO promoter. These findings clarify the epigenetic mechanism by which ClROS1-mediated DNA demethylation regulates flowering.

Chrysanthemum (Chrysanthemum morifolium) CmHRE2-like negatively regulates the resistance of chrysanthemum to the aphid (Macrosiphoniella sanborni).

BACKGROUND: The growth and ornamental value of chrysanthemums are frequently hindered by aphid attacks. The ethylene-responsive factor (ERF) gene family is pivotal in responding to biotic stress, including insect stress. However, to date, little is known regarding the involvement of ERF transcription factors (TFs) in the response of chrysanthemum to aphids. RESULTS: In the present study, CmHRE2-like from chrysanthemum (Chrysanthemum morifolium), a transcription activator that localizes mainly to the nucleus, was cloned. Expression is induced by aphid infestation. Overexpression of CmHRE2-like in chrysanthemum mediated its susceptibility to aphids, whereas CmHRE2-like-SRDX dominant repressor transgenic plants enhanced the resistance of chrysanthemum to aphids, suggesting that CmHRE2-like contributes to the susceptibility of chrysanthemum to aphids. The flavonoids in CmHRE2-like-overexpression plants were decreased by 29% and 28% in two different lines, whereas they were increased by 42% and 29% in CmHRE2-like-SRDX dominant repressor transgenic plants. The expression of Chrysanthemum-chalcone-synthase gene(CmCHS), chalcone isomerase gene (CmCHI), and flavonoid 3'-hydroxylase gene(CmF3'H) was downregulated in CmHRE2-like overexpression plants and upregulated in CmHRE2-like-SRDX dominant repressor transgenic plants, suggesting that CmHRE2-like regulates the resistance of chrysanthemum to aphids partially through the regulation of flavonoid biosynthesis. CONCLUSION: CmHRE2-like was a key gene regulating the vulnerability of chrysanthemum to aphids. This study offers fresh perspectives on the molecular mechanisms of chrysanthemum-aphid interactions and may bear practical significance for developing new strategies to manage aphid infestation in chrysanthemums.

A group VIIIa ethylene-responsive factor, CmERF4, negatively regulates waterlogging tolerance in chrysanthemum.

Ethylene-responsive factors (ERF) play an important role in plant responses to waterlogging stress. However, the function and mechanism of action of ERFVIII in response to waterlogging stress remain poorly understood. In this study, we found that expression of the ERF VIIIa gene CmERF4 in chrysanthemum was induced by waterlogging stress. CmERF4 localized to the nucleus when expressed in tobacco leaves. Yeast two-hybrid and luciferase assays showed that CmERF4 is a transcriptional inhibitor. CmERF4 overexpression in chrysanthemum reduced plant waterlogging tolerance, whereas overexpression of the chimeric activator CmERF4-VP64 reversed its transcriptional activity, promoting higher waterlogging tolerance than that observed in wild-type plants, indicating that CmERF4 negatively regulates waterlogging tolerance. Transcriptome profiling showed that energy metabolism and reactive oxygen species (ROS) pathway-associated genes were differentially expressed between CmERF4-VP64 and wild-type plants. RT-qPCR analysis of selected energy metabolism and reactive oxygen species-related genes showed that the gene expression patterns were consistent with the expression levels obtained from RNA-seq analysis. Overall, we identified new functions of CmERF4 in negatively regulating chrysanthemum waterlogging tolerance by modulating energy metabolism and ROS pathway genes.

Transcription factor DgMYB recruits H3K4me3 methylase to DgPEROXIDASE to enhance chrysanthemum cold tolerance.

Cold affects the growth and development of plants. MYB transcription factors and histone H3K4me3 transferase ARABIDOPSIS TRITHORAXs (ATXs) play important regulatory functions in the process of plant resistance to low-temperature stress. In this study, DgMYB expression was responsive to low temperature, and overexpression of DgMYB led to increased tolerance, whereas the dgmyb mutant resulted in decreased tolerance of Chrysanthemum morifolium (Dendranthema grandiflorum var. Jinba) to cold stresses. Interestingly, we found that only peroxidase (POD) activity differed substantially between wild type (WT), overexpression lines, and the mutant line. A DgATX H3K4me3 methylase that interacts with DgMYB was isolated by further experiments. DgATX expression was also responsive to low temperature. Overexpression of DgATX led to increased tolerance, whereas the dgatx mutant resulted in decreased tolerance of chrysanthemum to cold stresses. Moreover, the dgmyb, dgatx, and dgmyb dgatx double mutants all led to reduced H3K4me3 levels at DgPOD, thus reducing DgPOD expression. Together, our results show that DgMYB interacts with DgATX, allowing DgATX to specifically target DgPOD, altering H3K4me3 levels, increasing DgPOD expression, and thereby reducing the accumulation of reactive oxygen species (ROS) in chrysanthemum.

DgHDA6 enhances the cold tolerance in chrysanthemum by improving ROS scavenging capacity.

Histone deacetylases have been demonstrated to play an important role in responding to low-temperature stress, but the related response mechanism in chrysanthemum remains unclear. In this study, we isolated a cold-induced gene, DgHDA6, from chrysanthemum (Chrysanthemum morifolium Ramat). DgHDA6 contains 474 amino acids and shares a typical deacetylation domain with RPD3/HDA1 family members. The overexpression of DgHDA6 enhanced cold resistance in chrysanthemums. After low-temperature stress, the overexpression lines showed a higher survival rate. The contents of proline, soluble proteins and sugars, and the activities of antioxidant enzymes were significantly increased while the contents of H2O2, O2- and MDA were lower. Moreover, cold-stress-responding genes such as DgCuZnSOD, DgCAT, DgP5CS, and DgFAD were upregulated after cold stress. These results suggest that the overexpression of DgHDA6 can improve cold tolerance in chrysanthemum by enhancing ROS scavenging capacity.

Comparative Physiological and Transcriptome Analysis of Crossostephium chinense Reveals Its Molecular Mechanisms of Salt Tolerance.

Crossostephium chinense is a wild species with strong salt tolerance that has great potential to improve the salt tolerance of cultivated chrysanthemums. Conversely, the unique salt-tolerant molecular mechanisms of Cr. chinense are still unclear. This study performed a comparative physiological and transcriptome analysis of Cr. chinense, Chrysanthemum lavandulifolium, and three hybrids to investigate the salt-tolerant molecular mechanisms of Cr. chinense. The physiological results showed that Cr. chinense maintained higher superoxide dismutase (SOD) activity, alleviating oxidative damage to the membrane. KEGG enrichment analysis showed that plant hormone signaling transduction and the MAPK signaling pathway were mostly enriched in Cr. chinense and hybrids under salt stress. Further weighted gene co-expression network analysis (WGCNA) of DEGs suggested that abscisic acid (ABA) signaling transduction may play a significant role in the salt-tolerant mechanisms of Cr. chinense and hybrids. The tissue-specific expression patterns of the candidate genes related to ABA signaling transduction and the MAPK signaling pathway indicate that genes related to ABA signaling transduction demonstrated significant expression levels under salt stress. This study offers important insights into exploring the underlying salt-tolerant mechanisms of Cr. chinense mediated by ABA signaling transduction and broadens our understanding of the breeding strategies for developing salt-tolerant cultivars utilizing salt-tolerant chrysanthemum germplasms.

Increasing the Vase Life of Chrysanthemum Cut Flowers by Using Silver and Zinc Nanoparticles.

Cut flowers are horticultural products that have great potential to be developed. Efforts to maintain quality and extend the shelf life of cut flowers are very important to obtain a product that is accepted in the market. The main problems of chrysanthemum cut flowers are the leaves easily turning yellow, wilting, and failure to fully open flowers. This study aimed to obtain the best pulsing solution formulation that increases vase life and maintains the freshness of chrysanthemum cut flowers. Pulsing solution treatment was carried out on chrysanthemum cut flowers during the evaluation period. Pulsing solution treatment consisted of control, AgNO3, nano-Ag (NAg), ZnO, and nano-Zn (NZn). The results showed that NAg20 treatment increased the vase life of chrysanthemum cut flowers up to 23 days, which was 19 days longer than the control. Nano-Ag inhibits bacterial growth, flower wilting, color degradation, and carotenoids. In addition, nano-Ag increased the size of the bloom-flower diameter. Considering the results of all postharvest quality parameters mentioned above, NAg20 extends the vase life of chrysanthemum cut flowers.

Chrysanthemum coronarium L. Extract Attenuates Homocysteine-Induced Vascular Inflammation in Vascular Smooth Muscle Cells.

Hyperhomocysteinemia is a main risk factor for phenotypic modulation of vascular smooth muscle cells (VSMCs) and atherosclerosis. Phenotypic switching and proliferation of VSMCs are related to the progression of vascular inflammation. Chrysanthemum coronarium L. is a leafy vegetable with various biological functions, such as antioxidative, anti-inflammatory, and antiproliferative effects. In this study, we aimed to identify the mechanisms underlying the therapeutic and preventive effects of C. coronarium L. extract (CC) in regulating homocysteine (Hcy)-induced vascular inflammation in human aortic VSMCs. CC did not exhibit cytotoxicity and inhibited Hcy-stimulated VSMC proliferation and migration. In addition, CC promoted Hcy-induced expression of VSMC contractile phenotype proteins, including alpha-smooth muscle actin, calponin, and smooth muscle 22α. CC also decreased Hcy-induced accumulation of reactive oxygen species and expression of inflammatory markers nicotinamide adenine dinucleotide phosphate oxidase-4 and soluble epoxide hydrolase. These results showed that CC attenuates Hcy-induced inflammatory responses, highlighting its potential as a therapeutic or preventive target for Hcy-induced vascular inflammation.

CmNAC25 targets CmMYB6 to positively regulate anthocyanin biosynthesis during the post-flowering stage in chrysanthemum.

BACKGROUND: Anthocyanin is a class of important secondary metabolites that determines colorful petals in chrysanthemum, a famous cut flower. 'Arctic Queen' is a white chrysanthemum cultivar that does not accumulate anthocyanin during the flowering stage. During the post-flowering stage, the petals of 'Arctic Queen' accumulate anthocyanin and turn red. However, the molecular mechanism underlying this flower color change remains unclear. RESULTS: In this study, by using transcriptome analysis, we identified CmNAC25 as a candidate gene promoting anthocyanin accumulation in the post-flowering stage of 'Arctic Queen'. CmNAC25 is directly bound to the promoter of CmMYB6, a core member of the MBW protein complex that promotes anthocyanin biosynthesis in chrysanthemum, to activate its expression. CmNAC25 also directly activates the promoter of CmDFR, which encodes the key enzyme in anthocyanin biosynthesis. CmNAC25 was highly expressed during the post-flowering stage, while the expression level of CmMYB#7, a known R3 MYB transcription factor interfering with the formation of the CmMYB6-CmbHLH2 complex, significantly decreased. Genetic transformation of both chrysanthemum and Nicotiana tabacum verified that CmNAC25 was a positive regulator of anthocyanin biosynthesis. Another two cultivars that turned red during the post-flowering stages also demonstrated a similar mechanism. CONCLUSIONS: Altogether, our data revealed that CmNAC25 positively regulates anthocyanin biosynthesis in chrysanthemum petals during the post-flowering stages by directly activating CmMYB6 and CmDFR. Our results thus revealed a crucial role of CmNAC25 in regulating flower color change during petal senescence and provided a target gene for molecular design breeding of flower color in chrysanthemum.

Pullusurfactins A‒C, new biosurfactants produced by Aureobasidium pullulans A11231-1-58 from Chrysanthemum boreale Makino.

Biosurfactants have found widespread use across multiple industrial fields, including medicine, food, cosmetics, detergents, pulp, and paper, as well as the degradation of oil and fat. The culture broth of Aureobasidium pullulans A11231-1-58 isolated from flowers of Chrysanthemum boreale Makino exhibited potent surfactant activity. Surfactant activity-guided fractionation led to the isolation of three new biosurfactants, pullusurfactins A‒C (1‒3). Their chemical structures were established through the use of spectroscopic techniques, predominantly 1D and 2D NMR, in conjunction with mass measurements. We evaluated the surface tension activities of isolated compounds. At 1.0 mg l-1, these compounds showed high degrees of surfactant activity (31.15 dyne/cm, 33.75 dyne/cm, and 33.83 dyne/cm, respectively).

PHOTOLYASE/BLUE LIGHT RECEPTOR2 regulates chrysanthemum flowering by compensating for gibberellin perception.

The gibberellins (GAs) receptor GA INSENSITIVE DWARF1 (GID1) plays a central role in GA signal perception and transduction. The typical photoperiodic plant chrysanthemum (Chrysanthemum morifolium) only flowers when grown in short-day photoperiods. In addition, chrysanthemum flowering is also controlled by the aging pathway, but whether and how GAs participate in photoperiod- and age-dependent regulation of flowering remain unknown. Here, we demonstrate that photoperiod affects CmGID1B expression in response to GAs and developmental age. Moreover, we identified PHOTOLYASE/BLUE LIGHT RECEPTOR2, an atypical photocleavage synthase, as a CRYPTOCHROME-INTERACTING bHLH1 interactor with which it forms a complex in response to short days to activate CmGID1B transcription. Knocking down CmGID1B raised endogenous bioactive GA contents and GA signal perception, in turn modulating the expression of the aging-related genes MicroRNA156 and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3. We propose that exposure to short days accelerates the juvenile-to-adult transition by increasing endogenous GA contents and response to GAs, leading to entry into floral transformation.

Flowering repressor CmSVP recruits the TOPLESS corepressor to control flowering in chrysanthemum.

Plant flowering time is induced by environmental and endogenous signals perceived by the plant. The MCM1-AGAMOUSDEFICIENS-Serum Response Factor-box (MADS-box) protein SHORT VEGETATIVE PHASE (SVP) is a pivotal repressor that negatively regulates the floral transition during the vegetative phase; however, the transcriptional regulatory mechanism remains poorly understood. Here, we report that CmSVP, a chrysanthemum (Chrysanthemum morifolium Ramat.) homolog of SVP, can repress the expression of a key flowering gene, a chrysanthemum FLOWERING LOCUS T-like gene (CmFTL3), by binding its promoter CArG element to delay flowering in the ambient temperature pathway in chrysanthemum. Protein-protein interaction assays identified an interaction between CmSVP and CmTPL1-2, a chrysanthemum homologue of TOPLESS (TPL) that plays critical roles as transcriptional corepressor in many aspects of plant life. Genetic analyses revealed the CmSVP-CmTPL1-2 transcriptional complex is a prerequisite for CmSVP to act as a floral repressor. Furthermore, overexpression of CmSVP rescued the phenotype of the svp-31 mutant in Arabidopsis (Arabidopsis thaliana), overexpression of AtSVP or CmSVP in the Arabidopsis dominant-negative mutation tpl-1 led to ineffective late flowering, and AtSVP interacted with AtTPL, confirming the conserved function of SVP in chrysanthemum and Arabidopsis. We have validated a conserved machinery wherein SVP partially relies on TPL to inhibit flowering via a thermosensory pathway.

Lysine malonylation of DgnsLIPID TRANSFER PROTEIN1 at the K81 site improves cold resistance in chrysanthemum.

Lysine malonylation (Kmal) is a recently discovered posttranslational modification, and its role in the response to abiotic stress has not been reported in plants. In this study, we isolated a nonspecific lipid transfer protein, DgnsLTP1, from chrysanthemum (Dendranthema grandiflorum var. Jinba). Overexpression and CRISPR-Cas9-mediated gene editing of DgnsLTP1 demonstrated that the protein endows chrysanthemum with cold tolerance. Yeast 2-hybrid, bimolecular fluorescence complementation, luciferase complementation imaging, and coimmunoprecipitation experimental results showed that DgnsLTP1 interacts with a plasma membrane intrinsic protein (PIP) DgPIP. Overexpressing DgPIP boosted the expression of DgGPX (glutathione peroxidase), increased the activity of GPX, and decreased the accumulation of reactive oxygen species (ROS), thereby enhancing the low-temperature stress tolerance of chrysanthemum, while the CRISPR-Cas9-mediated mutant dgpip inhibited this process. Transgenic analyses in chrysanthemum showed that DgnsLTP1 improves the cold resistance of chrysanthemum in a DgPIP-dependent manner. Moreover, Kmal of DgnsLTP1 at the K81 site prevented the degradation of DgPIP in Nicotiana benthamiana and chrysanthemum, further promoted DgGPX expression, enhanced GPX activity, and scavenged excess ROS produced by cold stress, thereby further enhancing the cold resistance of chrysanthemum.

Terpenoid VOC profiles and functional characterization of terpene synthases in diploid and tetraploid cytotypes of Chrysanthemum indicum L.

Chrysanthemum indicum L. is a valuable medicinal plant with diploid and tetraploid forms that are widely distributed in central and southern China, and it contains abundant volatile organic compounds (VOCs). Despite the discovery of some terpene synthase (TPS) in C. indicum (i.e., CiTPS) in previous studies, many TPSs and their corresponding terpene biosynthesis pathways have yet to be discovered. In the present study, terpenoid VOCs in different tissues from two cytotypes of C. indicum were analyzed. We identified 52 types of terpenoid VOCs and systematically investigated the content and distribution of these compounds in various tissues. The two cytotypes of C. indicum exhibited different volatile terpenoid profiles. The content of monoterpenes and sesquiterpenes in the two cytotypes showed an opposite trend. In addition, four full-length candidate TPSs (named CiTPS5-8) were cloned from Ci-GD4x, and their homologous TPS genes were screened based on the genome data of Ci-HB2x. These eight TPSs displayed various tissue expression patterns and were discovered to produce 22 terpenoids, 5 of which are monoterpenes and 17 are sesquiterpenes. We further proposed corresponding terpene synthesis pathways, which can enable the establishment of an understanding of the volatile terpenoid profiles of C. indicum with different cytotypes. This knowledge may provide a further understanding of germplasm in C. indicum and may be useful for biotechnology applications of Chrysanthemum plants.

Overexpression of ClRAP2.4 in Chrysanthemum enhances tolerance to cold stress.

The apetala/ethylene responsive factor (AP2/ERF) family is one of the largest plant-specific transcription factors and plays a vital role in plant development and response to stress. The apetala 2.4 (RAP2.4) gene is a member of the AP2/ERF family. In this study, ClRAP2.4 cDNA fragment with 768bp open reading frame was cloned and the resistance of ClRAP2.4 overexpression to low temperature was investigated to understand whether RAP2.4 is involved in low-temperature stress in chrysanthemum (Chrysamthemum lavandulifolium ). Phylogenetic analysis showed that ClRAP2.4 belonged to the DREB subfamily and was most closely related to AT1G22190. ClRAP2.4 was localised in cell nucleus and promotes transcriptional activation in yeast. In addition, ClRAP2.4 was transformed by using the Agrobacterium -mediated leaf disc method, and four overexpression lines (OX-1, OX-2, OX-7, and OX-8) were obtained. The activities of superoxide dismutase and peroxidase, and proline content in leaves in the four overexpression line were higher than those in the wild type (WT), whereas the electrical conductivity and malondialdehyde content were decreased, indicating that the tolerance of plants with ClRAP2.4 overexpression to cold stress was increased. RNA-Seq showed 390 differentially expressed genes (DEGs) between the transgenic and WT plants(229 upregulated, 161 downregulated). The number of ABRE , LTR , and DRE cis -elements in the promoters of DEGs were 175, 106, and 46, respectively. The relative expression levels of ClCOR , ClFe/MnSOD , ClPOD , ClNCL , ClPLK , ClFAD , and ClPRP in the transgenic plants were higher than those in WT plants at low temperatures. These data suggest that ClRAP2.4 may increase chrysanthemum tolerance to cold stress.

KNOX Genes Were Involved in Regulating Axillary Bud Formation of Chrysanthemum × morifolium.

Branching is an important agronomic and economic trait in cut chrysanthemums. The axillary meristem (AM) formation of the axillary buds of cut chrysanthemums has a decisive role in its branching characteristics. However, little is known about the regulation mechanism of axillary meristem formation in chrysanthemums at the molecular level. Members of the Homeobox gene family especially genes belonging to the class I KNOX branch play a key role in regulating the axillary bud growth and development processes of plants. In this study, three genes belonging to the class I KNOX branch, CmKNAT1, CmKNAT6, and CmSTM were cloned from chrysanthemums, and their functions in regulating axillary bud formation were examined. The subcellular localization test showed that these three KNOX genes were expressed in the nucleus, so all of them might function as transcription factors. The results of the expression profile analysis showed that these three KNOX genes were highly expressed in the AM formation stage of axillary buds. Overexpression of KNOX genes result in a wrinkled leaf phenotype in tobacco and Arabidopsis, which may be related to the excessive division of leaf cells, resulting in the proliferation of leaf tissue. Furthermore, overexpression of these three KNOX genes enhances the regeneration ability of tobacco leaves, indicating that these three KNOX genes may participate in the regulation of cell meristematic ability, thus promoting the formation of buds. In addition, the results of fluorescence quantitative testing showed that these three KNOX genes may promote the formation of chrysanthemum axillary buds by promoting the cytokinin pathway while inhibiting the auxin and gibberellin pathways. In conclusion, this study demonstrated that CmKNAT1, CmKNAT6, and CmSTM genes were involved in regulating axillary bud formation of Chrysanthemum × morifolium and preliminarily revealed the molecular mechanism of their regulation of AM formation. These findings may provide a theoretical basis and candidate gene resources for genetic engineering breeding of new varieties of cut chrysanthemums without lateral branches.